Horse Gestation Calculator

320 to 370 days — a fifty-day window, the widest of any domestic animal.

Expected range320 to 370 daysa span of 50 days — this is a window, not a date

Days remaining40Horse, typically 340 days

Typical gestation340 days48.57 weeks

Earliest and latest from now20 to 70 days

Progress88.24%

Days elapsed300

Cat64 daysrange 61 to 70

Dog63 daysrange 58 to 68

Cow283 daysrange 279 to 292

Goat150 daysrange 145 to 155

Sheep147 daysrange 142 to 152

Pig114 daysrange 112 to 120

Rabbit31 daysrange 28 to 35

Guinea pig68 daysrange 59 to 72

Llama350 daysrange 335 to 365

Alpaca345 daysrange 335 to 355

Sperm can survive for days in the reproductive tract, so mating and fertilisation are not the same event. Counting from ovulation rather than from mating narrows this window considerably.

The formula

due date = mating date + typical gestation for the species

A window, not a date

Every figure here is the middle of a range that veterinary sources quote, and the ranges are genuinely wide. A dog may deliver anywhere from 58 to 68 days after mating; a mare's range runs from 320 to 370. Treating the central figure as a deadline rather than a midpoint is the most common mistake made with these numbers.

Mating is not conception

Sperm survives in the reproductive tract for days in several of these species, so the date of mating and the date of fertilisation can differ appreciably. In dogs the gap can be as much as a week, which is most of the reason the apparent gestation range is so wide. Counting from ovulation, measured properly, narrows it considerably.

Size does not settle it

Gestation length tracks how developed the young are at birth more than how big the mother is. A rabbit delivers helpless young in 31 days; a guinea pig, smaller still, takes 68 and produces young with fur and open eyes that can eat solid food almost immediately. The difference is a strategy, not a scaling law.

Ratios are expectations, not promises

Every genetic ratio on these pages is a probability distribution, not a guarantee. A 3:1 cross does not produce three dominant offspring for every recessive one in a litter of four — it produces each offspring independently with a three-quarters chance. Small families depart from the expected ratio routinely, and that is the reason Mendel needed thousands of pea plants rather than dozens.